System and print head for additive manufacturing system

ABSTRACT

A print head is disclosed for use in an additive manufacturing system. The print head may include a receiving end configured to receive a matrix and a continuous reinforcement, and a discharging end configured to discharge the continuous reinforcement at least partially coated in the matrix. The print head may also include a feeder located between the receiving end and the discharging end. The feeder may be configured to push the continuous reinforcement out of the print head at only select times during discharge of the continuous reinforcement and the matrix.

RELATED APPLICATIONS

This application is based on and claims the benefit of priority fromU.S. Provisional Application No. 62/656,155 that was filed on Apr. 11,2018, the contents of which are expressly incorporated herein byreference.

Technical Field

The present disclosure relates generally to a manufacturing system and,more particularly, to a print head for an additive manufacturing system.

BACKGROUND

Continuous fiber 3D printing (a.k.a., CF3D™) involves the use ofcontinuous fibers embedded within material discharging from a moveableprint head. A matrix is supplied to the print head and discharged (e.g.,extruded and/or pultruded) along with one or more continuous fibers alsopassing through the same head at the same time. The matrix can be atraditional thermoplastic, a liquid thermoset (e.g., a UV curable and/ortwo-part resin), or a combination of any of these and other knownmatrixes. Upon exiting the print head, a cure enhancer (e.g., a UVlight, an ultrasonic emitter, a heat source, a catalyst supply, etc.) isactivated to initiate and/or complete curing of the matrix. This curingoccurs almost immediately, allowing for unsupported structures to befabricated in free space. And when fibers, particularly continuousfibers, are embedded within the structure, a strength of the structuremay be multiplied beyond the matrix-dependent strength. An example ofthis technology is disclosed in U.S. Pat. No. 9,511,543 that issued toTyler on Dec. 6, 2016 (“the '543 patent”).

Although continuous fiber 3D printing provides for increased strength,compared to manufacturing processes that do not utilize continuous fiberreinforcement, care must be taken to ensure proper wetting of the fiberswith the matrix, proper cutting of the fibers, automated restartingafter cutting, proper compaction of the matrix-coated fibers afterdischarge, and proper curing of the compacted material. The disclosedprint head and system are directed at addressing one or more of theseissues and/or other problems of the prior art.

SUMMARY

In another aspect, the present disclosure is directed to another printhead for an additive manufacturing system. This print head may include areceiving end configured to receive a matrix and a continuousreinforcement, and a discharging end configured to discharge thecontinuous reinforcement at least partially coated in the matrix. Theprint head may also include a feeder located between the receiving endand the discharging end, the feeder being configured to push thecontinuous reinforcement out of the print head at only select timesduring discharge of the continuous reinforcement and the matrix

In another aspect, the present disclosure is directed to a system foradditively manufacturing a composite structure. The system may includeat least one of a gantry and a robotic arm that moves in a plurality ofdirections during manufacturing of the composite structure, and a headcoupled to the at least one of the gantry and the robotic arm. The headmay include a receiving end configured to receive a matrix and acontinuous reinforcement, and a discharging end configured to dischargethe continuous reinforcement at least partially coated in the matrix.The head may also include eccentric cam rollers located between thereceiving end and the discharging end. The eccentric cam rollers may beconfigured to push the continuous reinforcement out of the print headonly during a startup sequence.

In another aspect, the present disclosure is directed to another methodof additively manufacturing a composite structure. This method mayinclude receiving a matrix and a continuous reinforcement at a first endof a print head, and discharging the continuous reinforcement at leastpartially coated in the matrix from a second end of the print head. Themethod may also include pushing the continuous reinforcement out of theprint head at only select times during discharge of the continuousreinforcement and the matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosedmanufacturing system;

FIGS. 2 and 3 are diagrammatic illustrations of an exemplary disclosedhead that may be utilized with the manufacturing system of FIG. 1;

FIGS. 4 and 5 are diagrammatic illustrations of an exemplary guidingmodule that may form a portion of the print head of FIGS. 2 and 3;

FIGS. 6 and 7 are diagrammatic illustrations of an exemplary feedingmodule that may form a portion of the print head of FIGS. 2 and 3;

FIGS. 8 and 9 are diagrammatic illustrations of an exemplary cuttingmodule that may form a portion of the print head of FIGS. 2 and 3;

FIGS. 10, 11, and 12 are diagrammatic illustrations of an exemplarycompacting module that may form a portion of the print head of FIGS. 2and 3; and

FIG. 13 is a diagrammatic illustration of an exemplary curing modulethat may form a portion of the print head of FIGS. 2 and 3.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary system 10, which may be used tocontinuously manufacture a composite structure 12 having any desiredcross-sectional shape (e.g., circular, polygonal, etc.). System 10 mayinclude at least a support 14 and a print head (“head”) 16. Head 16 maybe coupled to and moved by support 14. In the disclosed embodiment ofFIG. 1, support 14 is a robotic arm capable of moving head 16 inmultiple directions during fabrication of structure 12, such that aresulting longitudinal axis of structure 12 is three-dimensional. It iscontemplated, however, that support 14 could alternatively be anoverhead gantry or a hybrid gantry/arm also capable of moving head 16 inmultiple directions during fabrication of structure 12. Although support14 is shown as being capable of multi-axis movements, it is contemplatedthat any other type of support 14 capable of moving head 16 in the sameor in a different manner could also be utilized. In some embodiments, adrive may mechanically couple head 16 to support 14, and includecomponents that cooperate to move and/or supply power or materials tohead 16.

Head 16 may be configured to receive or otherwise contain areinforcement that is at least partially coated in a matrix. The matrixmay include any type of material (e.g., a liquid resin, such as azero-volatile organic compound resin; a powdered metal; etc.) that iscurable. Exemplary matrixes include thermosets, single- or multi-partepoxy resins, polyester resins, cationic epoxies, acrylated epoxies,urethanes, esters, thermoplastics, photopolymers, polyepoxides, thiols,alkenes, thiol-enes, and more. In some instances, the matrix materialinside head 16 may need to be kept cool and/or dark in order to inhibitpremature curing or otherwise obtain a desired rate of curing afterdischarge. In other instances, the matrix material may need to be keptwarm for similar reasons. In either situation, head 16 may be speciallyconfigured (e.g., insulated, temperature-controlled, shielded, etc.) toprovide for these needs.

When multiple reinforcements are simultaneously used, the reinforcementsmay be of the same type and have the same diameter and cross-sectionalshape (e.g., circular, square, flat, etc.), or of a different type withdifferent diameters and/or cross-sectional shapes. The reinforcementsmay include, for example, carbon fibers, vegetable fibers, wood fibers,mineral fibers, glass fibers, metallic wires, optical tubes, etc. Itshould be noted that the term “reinforcement” is meant to encompass bothstructural and non-structural types of continuous materials that can beat least partially encased in the matrix discharging from head 16. Thematrix, dry reinforcements, and/or reinforcements that are alreadyexposed to the matrix (e.g., wetted reinforcements) may be transportedinto head 16 in any manner apparent to one skilled in the art.

The matrix material and/or reinforcement may be discharged from head 16via at least two different modes of operation. In a first mode ofoperation, the matrix material and/or reinforcement are extruded (e.g.,pushed under pressure and/or mechanical force) from head 16 as head 16is moved by support 14 to create the 3-dimensional trajectory within alongitudinal axis of structure 12. In a second mode of operation, atleast the reinforcement is pulled from head 16, such that a tensilestress is created in the reinforcement during discharge. In this mode ofoperation, the matrix material may cling to the reinforcement andthereby also be pulled from head 16 along with the reinforcement, and/orthe matrix material may be discharged from head 16 under pressure alongwith the pulled reinforcement. In the second mode of operation, wherethe matrix material is being pulled from head 16 with the reinforcement,the resulting tension in the reinforcement may increase a strength ofstructure 12 (e.g., by aligning the reinforcements, inhibiting buckling,equally distributing loads, etc.), while also allowing for a greaterlength of unsupported structure 12 to have a straighter trajectory. Thatis, the tension in the reinforcement remaining after curing of thematrix material may act against the force of gravity (e.g., directlyand/or indirectly by creating moments that oppose gravity) to providesupport for structure 12.

The reinforcement may be pulled from head 16 as a result of head 16moving away from an anchor point 18. In particular, at the start ofstructure formation, a length of matrix-impregnated reinforcement may bepulled and/or pushed from head 16, deposited onto anchor point 18, andcured such that the discharged material adheres (or is otherwisecoupled) to anchor point 18. Thereafter, head 16 may be moved away fromanchor point 18, and the relative movement may cause the reinforcementto be pulled from head 16. It should be noted that the movement ofreinforcement through head 16 could be assisted (e.g., via internal headmechanisms), if desired. However, the discharge rate of reinforcementfrom head 16 may primarily be the result of relative movement betweenhead 16 and anchor point 18, such that tension is created within thereinforcement. It is contemplated that anchor point 18 could be movedaway from head 16 instead of or in addition to head 16 being moved awayfrom anchor point 18.

One or more cure enhancers (e.g., one or more light sources, anultrasonic emitter, a laser, a heater, a catalyst dispenser, a microwavegenerator, etc.—not shown in FIG. 1) may form a portion of head 16 andbe configured to enhance a cure rate and/or quality of the matrix as itis discharged from head 16. The cure enhancer(s) may be controlled toselectively expose internal and/or external surfaces of structure 12 toenergy (e.g., light energy, electromagnetic radiation, vibrations, heat,a chemical catalyst or hardener, etc.) during the formation of structure12. The energy may increase a rate of chemical reaction occurring withinthe matrix, sinter the material, harden the material, or otherwise causethe material to cure as it discharges from head 16.

A controller 21 may be provided and communicatively coupled with support14 and head 16. Controller 21 may embody a single processor or multipleprocessors that include a means for controlling an operation of system10. Controller 21 may include one or more general- or special-purposeprocessors or microprocessors. Controller 21 may further include or beassociated with a memory for storing data such as, for example, designlimits, performance characteristics, operational instructions, matrixcharacteristics, reinforcement characteristics, characteristics ofstructure 12, and corresponding parameters of each component of system10. Various other known circuits may be associated with controller 21,including power supply circuitry, signal-conditioning circuitry,solenoid/motor driver circuitry, communication circuitry, and otherappropriate circuitry. Moreover, controller 21 may be capable ofcommunicating with other components of system 10 via wired and/orwireless transmission.

One or more maps may be stored in the memory of controller 21 and usedduring fabrication of structure 12. Each of these maps may include acollection of data in the form of models, lookup tables, graphs, and/orequations. In the disclosed embodiment, the maps are used by controller21 to determine desired characteristics of the cure enhancer(s), theassociated matrix, and/or the associated reinforcements at differentlocations within structure 12. The characteristics may include, amongothers, a type, quantity, and/or configuration of reinforcement and/ormatrix to be discharged at a particular location within structure 12,and/or an amount, intensity, shape, and/or location of desired curing.Controller 21 may then correlate operation of support 14 (e.g., thelocation and/or orientation of head 16) and/or the discharge of materialfrom head 16 (a type of material, desired performance of the material,cross-linking requirements of the material, a discharge rate, etc.),such that structure 12 is produced in a desired manner

An exemplary head 16 is disclosed in greater detail in FIGS. 2 and 3.Head 16 may include, among other things, a housing 20 that is configuredto hold, enclose, contain, or otherwise provide mounting for a guidingmodule 22, a feeding module 24, a cutting module 26, a compacting module28, and a curing module 30. It should be noted that additional and/ordifferent modules (e.g., a fiber storage module, a tension managementmodule, an impregnation module, etc.) could be included, if desired. Aswill be described in more detail below, the matrix, dry reinforcements,and/or matrix-wetted reinforcements described above may be received viaguiding module 22, selectively advanced by feeding module 24, severed bycutting module 26, compressed by compacting module 28, and hardened orotherwise cured by curing module 30.

Housing 20 may include any number of panels connected to each other toform a multi-sided enclosure that supports the remaining components ofhead 16, while also restricting penetration of ambient energy (e.g., UVlight), which could negatively affect print quality. In the disclosedembodiment, the enclosure is generally four-sided, having a receiving orupper end 32 and a discharging or lower end 34 that are both at leastpartially open. It is contemplated that the enclosure may have a greateror lesser number of sides, if desired. The four sides of housing 20 mayinclude a lead panel 36, a trail panel 38 located opposite lead panel36, a side panel 40 fixed (e.g., bolted, welded, chemically bonded, orotherwise integrally fabricated) between lead and trail panels 36, 38,and a door 42 (omitted from FIG. 3 for clarity) located opposite sidepanel 40. Door 42 may be pivotally connected to one of lead and trailpanels 36, 38 via one or more hinges 44, and selectively connected tothe other of lead and trail panels 36, 38 via a latch (e.g., a magneticlatch) 46. It is contemplated, however, that other means of removablyconnecting door 42 to the rest of housing 20 could be implemented.

Lead panel 36 may be located at a leading side of head 16, relative to anormal travel direction (represented by an arrow 48) of head 16. Leadpanel 36 may embody a flat plate having a generally rectangular shape,although other contours and shapes are contemplated. A width of leadpanel 36 may be narrower than a length thereof (e.g., less than ½ of thelength), and a thickness of lead panel 36 may be less than the width.Receiving end 32 of lead panel 36 may have a square edge, whiledischarging end 34 of lead panel 36 may be chamfered inward. A pluralityof through-holes may be formed around a perimeter of lead panel 36 foruse in connecting lead panel 36 to the other panels. In addition, anynumber of through- and/or blind-holes may be formed within a centerfield of lead panel 36 for use in mounting any of the above-listedmodules.

Trail panel 38 may be located at a trailing side of head 16, relative tothe normal travel direction of head 16. Trail panel 38, like lead panel36, may embody a flat plate having a generally rectangular shape. Trailpanel 38 may have the same general width and thickness as lead panel 36,but a greater length. Receiving end 32 of trail panel 38 may have asquare edge that is generally aligned with the square edge of lead panel36, while discharging end 34 of trail panel 38 may extend past thechamfered edge of lead panel 36. Discharging end 34 of trail panel 38may or may not be chamfered. A plurality of through-holes may be formedaround a perimeter of trail panel 38 for use in connecting trail panel38 to the other panels. In addition, any number of through- and/orblind-holes may be formed within a center field of trail panel 38 foruse in mounting any of the above-listed modules.

Side panel 40 and door 42 may be substantially identical in shape andsize. Each of side panel 40 and door 42 may embody a flat plate having apolygonal shape, with receiving end 32 being generally square anddischarging end 34 being angled. Discharging ends 34 of side panel 40and door 42 may have square edges that extend from the chamfered edge oflead panel 36 to the square edge of trail panel 38. A plurality ofthrough-holes may be formed around the perimeters of side panel 40and/or door 42 for connection to lead and/or trail panels 36, 38. Inaddition, any number of through- and/or blind-holes may be formed withincenter fields of side panel 40 and/or door 42 for use in mounting any ofthe above-listed modules.

As shown in FIG. 3, guiding module 22 may be located generally atreceiving end 32 of housing 20. In some embodiment, guiding module 22may extend out of housing 20 a distance past receiving end 32. In otherembodiments, portions of guiding module 22 may extend (e.g., partiallyor completely) to feeding module 24, such that matrix-wettedreinforcements are supported and/or guided for a greater length insideof head 16. It is also contemplated that guiding module 22 (or a similarwetting module) could be located closer to feeding module 24 thanreceiving end 32 or be completely outside of housing 20 and upstream ofhead 16, if desired.

Guiding module 22 may include components that cooperate to receivematrix, dry reinforcements, and/or matrix-wetted reinforcements atreceiving end 32 of housing 20, and to combine, support, and/or guidethe materials to feeding module 24. As shown in FIGS. 4 and 5, thesecomponents may include, among other things, a base 50, one or moreentrant rollers 52 operatively connected to an end of base 50, and apiloting subassembly 54 located opposite entrant roller(s) 52. Thereinforcements (e.g., dry and/or matrix-wetted reinforcements) may passfirst over entrant roller(s) 52 and then through piloting subassembly54, where the reinforcements are aligned in a desired sequence andorientation, and caused to converge (e.g., such that a small gap or nogap exists between adjacent reinforcements).

It should be noted that, in some embodiments, matrix may be first orsupplementally introduced to the reinforcements by guiding module 22.For example, as the reinforcements pass through rollers 53 and/or intopiloting subassembly 54, matrix may be applied to the reinforcements.The reinforcements may pass through a matrix bath, pass through a matrixflow, be sprayed with matrix, or otherwise receive at least a partiallycoating of matrix (e.g., a layer of matrix on at least one side). Insome embodiments, contact with rollers 53 and/or surfaces withinpiloting subassembly 54 (e.g., surfaces that extend into a straight-linetrajectory of the reinforcements, causing the reinforcements to bediverted) may generate a pressure differential through thereinforcements that urges the matrix coating to disburse and/or flowthrough the reinforcements. As the reinforcements exit guiding module22, the reinforcements may be fully wetted with a desired amount ofmatrix. Any excess matrix and/or reinforcement debris (e.g., fibershards, dust, etc.) may drip or be forced (e.g., pushed and/or pulled)off the reinforcements inside of or just downstream of guiding module22. In some embodiments, a low-pressure area within guiding module 22may help to remove the excess matrix. It is contemplated that a rate ofmatrix application may be coordinated with a volumetric rate ofreinforcements passing through guiding module 22, such that the need toremove excess matrix is reduced.

Base 50 of piloting subassembly 54 may function as a mounting platformfor the remainder of guiding module 22, and itself be removablyconnected to housing 20 (referring to FIGS. 2 and 3). For example, base50 may include a back portion 56 that extends lengthwise in the generaldirection of reinforcement-travel through guiding module 22 (indicatedby an arrow 58), from an entrance end 60 to an exit end 62. Base 50 maybe connectable to housing 20 (e.g., to side panel 40) in any mannerknown in the art (e.g., via threaded fasteners, quick-release couplings,and other similar mechanisms 63), such that guiding module 22 canperiodically be removed as an integral unit for adjustment, cleaning,repair, and/or replacement. One or more ears 64 may extend in a normaldirection from back portion 56 at entrance end 60, and entrant roller(s)52 may be rotatably connected between distal ends of ears 64 (e.g., viacorresponding pins 66, bearings—not shown, bushings—not shown, and/orset screws 68). Piloting subassembly 54 may be mounted to back portion56 at exit end 62 (e.g., at a same side from which ears 64 extend) inany manner known in the art (e.g., via one or more threaded fasteners70). In one embodiment, base 50 is fabricated from a low-weight and/orlow-friction material (e.g., aluminum, Teflon, Delrin, nylon, etc.),such that a weight of head 16 may be kept low. In other embodiments,however, base 50 may be fabricated from a ferromagnetic material (e.g.,iron, stainless steel, etc.), for magnetic use with piloting subassembly54 (described in more detail below).

Entrant roller(s) 52 may be fabricated from a relatively compliantand/or low-friction type of material. For example, entrant roller(s) 52may be fabricated from aluminum, steel, Delrin, Teflon, nylon, oranother similar material known in the art. Entrant roller(s) 52 may havea diameter of about 0.25-5.0″, and an outer annular surface that issmooth, porous, or roughened (e.g., knurled) to reduce drag, inhibitfiber breakage and/or separation, maintain orientation and/or integrityof the fibers, and to reduce wear. It is contemplated that, in someinstances, a scraper and/or catch reservoir could be associated withentrant roller(s) 52, if desired, to remove and/or collect excess resin.In applications that utilize multiple entrant rollers 52, it iscontemplated that entrant rollers 52 may be biased towards each other(e.g., by a spring—not shown) and used to squeeze out excess resin (ifalready applied to the reinforcements passing therethrough). In theseapplications, it may be helpful to drive entrant rollers 52 and therebyreduce drag. A location of (e.g., a spacing between) entrant roller(s)52 may be adjustable.

It should be noted that, although a single entrant roller 52 isillustrated at each side of the reinforcements passing thereby, it iscontemplated that multiple separate rollers (e.g., one roller perreinforcement or reinforcement grouping) could alternatively be used.This may allow for entrant roller(s) 52 to accommodate different travelspeeds of the reinforcements that are experienced during cornering ofhead 16.

Piloting subassembly 54 may include multiple components that cooperateto keep individual reinforcements within a desired alignment andtransverse sequence as they pass out of head 16 (e.g., by way of feedingmodule 24, cutting module 26, and compacting module 28), while alsocausing the individual reinforcements to converge transversely towardseach other for reduced porosity. These components may include, amongother things, a channeling base 72, a cover 74, and a latching mechanism76. Channeling base 72 may have a leading end 78 and a trailing end 80,with inner and outer primary surfaces that extend therebetween. Theouter surface of channeling base 72 may mate against back portion 56 ofbase 50, while the inner surface may engage (e.g., continuously or onlyperiodically) the wetted reinforcements as they pass through pilotingsubassembly 54. Edges of the inner surface at one or both of leading andtrailing ends 78, 80 may be rounded to reduce a likelihood of damagingthe reinforcements. Cover 74 may have an inner surface that issubstantially identical to and oriented in mirrored-opposition to theinner surface of channeling base 72.

In one embodiment, any number of fiber-separating and/orpressure-generating features (e.g., dividers, channels, grooves, vanes,fins, rollers, lobes, etc.) 82 may be formed within a space betweenchanneling base 72 and cover 74. Features 82 may be integral withchanneling base 72 and/or cover 74 (e.g., extending inward), orcompletely separate components, as desired. Features 82 may extend inthe reinforcement-travel direction, and be spaced at regular intervalsin a transverse direction. The spacing between features 82 maycorrespond with a desired fiber-to-resin ratio. For example, a desiredratio of 60% may drive a cross-sectional area in the spacing betweenfeatures 82 to be about 40% greater than a cross-sectional area ofreinforcements passing through the spacing allowing for the area notfilled with reinforcements to be filled with matrix. In someembodiments, a width direction (relative to a resulting ribbon) of thecross-sectional area between features is greater than a thicknessdirection, such that more matrix is deposited between reinforcementsrather than at an outer surface of the ribbon. It is contemplated thatfeatures 82 may be generally parallel with each other along their entirelength, or converge toward the exit end of piloting subassembly 54. Forexample, a spacing between features 82 may decrease along their length.For example, a taper angle of features 82 may be about 0-10°. Inaddition, in some embodiments, a spacing between channeling base 72 andcover 74 may remain consistent in the reinforcement-travel direction, ordecrease to provide for greater convergence of thewetted-reinforcements. Features 82 may be fabricated from a low-frictionmaterial (e.g., aluminum, Delrin, Teflon, nylon, etc.), and a spacingbetween features may be about 0.02-1.0″. It is contemplated thatfeatures 82 may be interconnected (e.g., via a webbing or a plate) andreplaceable as a single unit (e.g., for a unit having differentspacings, sizes, shapes, materials, etc.).

Cover 74 may be held in a particular location and/or orientationrelative to channeling base 72 by way of latching mechanism 76, suchthat the matrix-wetted reinforcements passing through guiding module 22are trapped between cover 74 and channeling base 72. It is contemplatedthat any type of latching mechanism may be used for this purpose. In thedisclosed embodiment, latching mechanism 76 is a magnetic-type ofmechanism. Specifically, latching mechanism 76 may include at least onemagnet (e.g., base and cover magnets 84, 86) associated with at leastone of channeling base 72 and cover 74. Base magnet 84 may be trappedbetween channeling base 72 and back portion 56 of base 50 (e.g., withina recess 88 of channeling base 72). Cover magnet 86 may similarly betrapped within a recess 90 of cover 74, for example via a lid 92 that isremovably connected to cover 74 (e.g., via threaded fasteners 94). Itshould be noted that, while two magnets (e.g., base and cover magnets84, 86) are shown as being centered over a travel path of thereinforcements, a greater or lesser number of magnets may be used andlocated outward from the travel path (e.g., at the sides of the travelpath), if desired. During operation, cover 74, cover magnet 86, lid 92,and fastener 94 may together be removed as a single unit from the restof piloting subassembly 76 for easier threading of the matrix-wettedreinforcements through guiding module 22. It is also contemplated thatcover 74, cover magnet 86, lid 92, and fastener 94 could be a singleintegral component, if desired. Likewise, back portion 56, channelingbase 72, base magnet 84, and fastener 70 could be a single integralcomponent, if desired.

Feeding module 24 may receive (e.g., pull) the matrix-wettedreinforcements from guiding module 22 and selectively push thereinforcements further through head 16 (e.g., through cutting module 26to compacting module 28). As shown in FIGS. 6 and 7, feeding module 24may be an assembly of multiple components. These components may include,among other things, a base 96, one or more rollers 98 operativelysupported by base 96, and a drive 100 that is operatively connected tobase 96 and configured to power the rotation of roller(s) 98.

Base 96 may function as a mounting platform for the remainder of feedingmodule 24, and itself be removably connected to housing 20 (referring toFIGS. 2 and 3). For example, base 96 may include a back portion 102 thatextends lengthwise in the general direction of reinforcement-travelthrough feeding module 24 (indicated by an arrow 104). Base 96 may beconnectable to housing 20 (e.g., to side panel 40) in any manner knownin the art (e.g., via threaded fasteners—not shown), such that feedingmodule 24 can periodically be removed as an integral unit foradjustment, cleaning, repair, and/or replacement. One or more ears 106may extend in a normal direction from back portion 102, and a yoke 108may be rotatably connected between distal ends of ears 106 (e.g., viacorresponding pins 110, bearings 112, and/or set screws 114). In someembodiments, a spring (not shown) may be located to rotationally biasyoke 108 toward back portion 102.

In the disclosed embodiments shown in FIGS. 6 and 7, two feed rollers 98are utilized, including a directly driven roller 98A and a slave roller98B. One of rollers 98A, 98B (e.g., directly driven roller 98A) may bepivotally mounted to back portion 102 of base 96 (e.g., at an endopposite ears 106), while the other of rollers 98A, 98B (e.g., slavedrive roller 98B) may be pivotally mounted to a distal end of yoke 108.Rollers 98 may be connected to base 96 and/or yoke 108 via cantileveredaxles 116, bearings (not shown), bushings, splines, clips (not shown),set screws (not shown), spacers, keyways, end-stops, etc., such thatrollers 98 are maintained in general alignment with entrant roller 52and features 82 in guiding module 22.

At least one of rollers 98 may be an eccentric wheel, cylinder, or camhaving an irregular shape that imparts movement to thewetted-reinforcement only during part of the roller's rotation. Forexample, FIGS. 6 and 7 illustrate an outer periphery of each roller 98as including a first portion 118 having a substantially constant radius,and a remaining portion 120 having a reduced radius (e.g., a constantreduced radius, a variably reduced radius, and/or one or more connectedsplines or linear segments located closer to an axis or rotation thanthe radius of first portion 118). During operation, rollers 98A and 98Bmay be synchronized, such that transition points between the first andremaining portions 118, 120 pass through a straight line drawn betweenthe axes of rollers 98A, 98B at the same time. With this configuration,any time that any part of first portions 118 are passing through thestraight line between the axes of rollers 98A, 98B, the rollers arecontacting and exerting force on the wetted-reinforcements. And incontrast, any time that any part of remaining portions 120 are passingthrough the straight line between the axes of rollers 98A, 98B, aclearance exists around the wetted-reinforcements (i.e., no force isbeing exerted). The spring described above may bias rollers 98 towardseach other, particularly during pushing of the matrix-wettedreinforcement, such that rollers 98 are able to adequately grip thereinforcement. It is contemplated that only one of rollers 98 may beeccentric or cam-like and driven, while the other roller 98 isconcentric, pliable, and only rotates when the larger-diameter portionof the eccentric roller 98 is engaged therewith. It is also contemplatedthat a pair of rollers 98 may be provided separately for each individualtow of reinforcements passing through feeding module 24, if desired.

Rollers 98 may primarily be used during start of a new printing event,when a free end of matrix-wetted reinforcement must be pushed out ofhead 16. An arc length of first portion 118 may be selected to push adesired length of matrix-wetted reinforcement from head 16 for start ofthe new printing event. In one embodiment, this arc length may be aboutequal to or greater than a distance between cutting module 26 (e.g., acut location within cutting module 26) and compacting module 28 (e.g., acompacting location at compacting module 28).

Rollers 98, like entrant roller(s) 52, may be fabricated from arelatively compliant and/or low-friction type of material. For example,rollers 98 may be fabricated from aluminum, steel, Delrin, Teflon,nylon, urethane, or another similar material known in the art. Rollers98 may have a diameter of about 0.25-5.0″, and an outer annular surfacethat is porous and/or roughened (e.g., knurled) to provide traction,and/or to maintain orientation and/or integrity of the fibers. It iscontemplated that, in some instances, a scraper and/or catch reservoircould be associated with rollers 98, if desired, to remove and/orcollect excess resin. In some applications, a location of (e.g., aspacing between) entrant rollers 98 may be adjustable. It is alsocontemplated that a blade or other cutting mechanism (not shown) couldform a portion of one or both of rollers 98, if desired.

Drive 100 may be configured to selectively power the rotation of rollers98. Drive 100 may include, among other things, an actuator 122, and alinkage 124 operatively connecting actuator 122 to one or both ofrollers 98. In the disclosed embodiment, actuator 122 is a motor (e.g.,an electric stepper motor). It is contemplated, however, that othertypes of actuators could be used, if desired. Linkage 124 may includeany component(s) known in the art for connecting an actuator to aroller. In the disclosed example, linkage 124 includes a stub-shaft 126configured to engage (e.g., internally engage) the axle 116 associatedwith roller 98A for direct drive or roller 98A. Linkage 124 mayadditionally include a gear train (e.g., two or more intermeshing spuror helical gears) and/or belt/pulley arrangement 128 that links therotation of roller 98A with the rotation of roller 98B. Any number andtype of hardware components (e.g., mounting plates, spacers, bushings,clips, fasteners, etc.) 130 may be used to connect actuator 122 with therest of feeding module 24 and or housing 20.

Cutting module 26 may be located between feeding module 24 andcompacting module 28 (referring to FIGS. 2 and 3), and configured toselectively sever the reinforcements passing therethrough. As can beseen in FIGS. 8 and 9, cutting module 26 may include, among otherthings, a frame 132, a blade 134 secured within frame 132, an anvil 136moveable relative to frame 132, and an actuator 138 configured to moveanvil 136. Frame 132 may include a leading component 140 that isremovably connected (e.g., via fasteners 142) to a trailing component146 (i.e., relative to a travel direction of the reinforcements throughhead 16, represented by an arrow 148). Leading and trailing components140, 146 may be generally rectangular plates having aligned centralopenings 150 through which the reinforcements travel. A trailing primarysurface of leading component 140 may be configured to mate against aleading primary surface of trailing component 144, and one or morechannels 152 may be formed at the interface (e.g., at opposing edges ofcentral opening 150). Channel(s) 152 may function as guides in whichanvil 136 slides towards and away from the reinforcements and blade 134.In the disclosed embodiment, channels 152 are stepped to accommodatecorresponding steps formed within opposing edges of anvil 136 (describedin more detail below). It is contemplated, however, that channels 152may be devoid of steps, if desired. Frame 132 may be connected tohousing 20 (referring to FIG. 1) via one or more fasteners 154.

Blade 134 may be rigidly connected to frame 132 (e.g., sandwichedbetween leading and trailing components 140, 144), and orientedtransversely to the travel direction of the reinforcements. A cuttingedge 156 of blade 134 may include sharpened serrations that function tograsp and cut individual or groups of individual reinforcements. In oneembodiment, the reinforcements have a diameter in the range of 1.82E-4in to 1.48E-3 in, and the serrations (e.g., an inter-peak orinter-valley distance of the serrations) of cutting edge 156 may besized and separated by a distance that ensures proper cutting withoutsignificant reinforcement movement. For example, a diameter of a singlereinforcement or group of reinforcements (e.g., tow) may be wider (e.g.by about 0.005-0.020″) than a whole-number-multiple of the diameter of aserration of blade 134.

Anvil 136 may be pushed and/or pulled by actuator 138 in a directionsubstantially orthogonal to the travel direction of the reinforcements,such that the reinforcements are urged radially against the serrationsof blade 134. In the disclosed embodiment, anvil 136 is generallyrectangular and plate-like, having a tip end oriented toward blade 134and an opposing base end oriented toward actuator 138. In the disclosedembodiment, the tip end of anvil 136 is offset in the travel directionof the reinforcements (e.g., relative to a body or shaft portion) by anamount about equal to a thickness of anvil 136. In addition, the tip endmay be chamfered away from blade 134 to inhibit binding of the tip endwith the reinforcements. The chamfer may have an angle of about 5-90°and a length of about 1-1.5 inches. Although the disclosed exampleillustrates anvil 136 as being a single-piece unit, it is contemplatedthat anvil 136 could alternatively be a multi-piece assembly, ifdesired. For example, the tip end of anvil 136 could be separate fromthe rest of anvil 136. The tip of anvil 136 may be made from a hardenedtool steel, a silicon carbide, or another ceramic. In some instances,lubrication may be selectively applied to anvil 136, if desired. Forexample, a Teflon-based grease or another type of lubrication may bemanually and/or automatically (e.g., via a pressure or drip system—notshown) disposed within channels 152.

Actuator 138 is illustrated in FIGS. 8 and 9 as being a pneumatic linearactuator, having a piston 158 connected (e.g., in any rigid, flexible,and/or pivotal manner known in the art) to a base end of anvil 136. Asair (or another pressurized medium) is applied to correspondingchamber(s) within a cylinder 160, piston 158 may be caused to movelinearly in and/or out of cylinder 160. It is contemplated that actuator138 may be a single-acting device having a return mechanism (e.g., aspring), or a double-acting device, as desired. A stroke-length, speed,and/or force of actuator 138 may be adjustable (e.g., by adjusting amedium flow rate, a medium pressure, an end-stop location, etc.). It iscontemplated that another type of mechanism (e.g., a hydraulic piston, asolenoid-driven plunger, a motor/lead-screw combination, motor/cam,etc.) may alternatively be used as actuator 138, in some embodiments.Cylinder 160 may be rigidly connected to housing 20 (e.g., to trailpanel 38) via any number of threaded fasteners (not shown). In oneembodiment, cylinder 160 is a pneumatic cylinder having an internal boreof about 0.10-1.0 inches.

FIGS. 10, 11, and 12 illustrate various views of an exemplary compactingmodule 28. As shown in these figures, compacting module 28 may be aself-contained assembly of multiple components that interact toselectively compact the wetted-reinforcements during discharge from head16. These components may include, among other things, a frame 162, acompactor 164 operatively mounted at least partially within frame 162,and an actuator 166 configured to selectively move compactor 164 betweenvarying levels of compaction. Frame 162 may be a monolithic structurehaving an end surface 168 that is removably connected to housing 20(e.g., to trail panel 38—referring to FIGS. 2 and 3). A cross-section offrame 162 may have an I-shape, when viewed from the perspective of endsurface 168. Opposing end-flanges of the I-shape may extend in thetravel direction of the reinforcements through head 16. At least one ofthe end-flanges may have a groove 170 formed at an inside surface thatis configured to receive a sliding pin 172 of compactor 164 (e.g., atonly one end of compactor 164) and guide, as well as limit, the motionof compactor 164 imparted by actuator 166. Similarly, one or moresliding pins 174 may extend inward from one or both of the end-flangesto engage groove(s) 176 of compactor 164 to guide and/or limit motion ofcompactor 164 (e.g. from opposing ends) relative to frame 162.

Compactor 164 may be disposed between the end-flanges of frame 162, andextend from the discharge end of housing 20 (referring to FIGS. 2 and3). In other words, compactor 164 may form a tip and tool center point(TCP) of head 16. In the disclosed embodiments, head 16 is nozzle-less.Accordingly, the discharge location of head 16 may correspond with aline of contact between compactor 164 and a print surface (e.g., wherecompactor 164 pushes the wetted-reinforcements onto the surface). Itshould be noted that the line of contact may shift, for example as head16 is tilted by support 14 (referring to FIG. 1) relative to the printsurface and/or relative to a travel direction (e.g., if printing intofree-space).

Because compactor 164 may form the tip and TCP of head 16, a form factorof head 16 may be at least partially defined by a spatial relationshipbetween compactor 164 and the surrounding components (e.g., housing 20)that extend outward from a center line (e.g., from the reinforcementtravel path) of head 16. This form factor may be represented by an angleα (shown only in FIG. 3). Angle α may represent the angle of a smallestinternal corner between adjacent surfaces in which head 16 may be fullyfunctional. In the disclosed embodiments, α may be less than about 90°(e.g., about 80-90°).

Compactor 164 may include a roller 178 that is held within a bracket 180(e.g., via an axle 182 and any number of bearings, bushings, clips, setscrews, etc.—not shown). Roller 178, like entrant roller(s) 52, may befabricated from a relatively compliant and/or low-friction type ofmaterial. For example, roller 178 may be fabricated from aluminum,steel, Delrin, Teflon, nylon, or another similar material known in theart. Roller 178 may have a diameter of about 0.25-5.0″, and an outerannular surface that is smooth, porous, or roughened (e.g., knurled) toreduce drag, to provide a desired surface texture, to reduce fiber wearor breakage, to retain and/or dispense additional matrix, etc. It iscontemplated that, in some instances, a scraper (not shown) could beassociated with roller 178, if desired, to remove excess resin. In someapplications, a location of roller 178 may be adjustable. Pin 172 mayextend outward from a first side of bracket 180 to engage groove 170 offrame 162, while grooves 176 may be formed within the first side ofbracket 180 and in a second side at an opposing end of roller 178.During operation of actuator 166, roller 178 may be caused to movetogether with bracket 180 relative to frame 162.

The movement of compactor 164 initiated by actuator 166 may includesequential linear and rotational motions. The linear motion may affect apressure applied by roller 178 on the discharging material, while therotational motion may affect engagement of roller 178 with the material.For example, when actuator 166 is in a most-retracted state, roller 178may be pulled a greatest linear distance into housing 20 and alsorotated away from the discharging reinforcements. This retracted statemay provide a greatest clearance for purposes of threading thereinforcements through head 16. As actuator 166 is extended, roller 178may first be rotated from the retracted state to an engaged stateagainst the discharging reinforcements. Further extension of actuator166 may then affect a pressure applied by roller 178 on thereinforcements, with a greater extension corresponding with a greaterpressure, and vice versa.

In one embodiment, roller 178 may have a rotation range/clearance, and atranslation range. These ranges may be affected by the geometry ofgrooves 170 and 176. For example, a length of groove 170 may correspondwith the translation range, while an arc length and/or curvature radiusof grooves 176 may correspond with the rotational range and/orclearance.

Actuator 166 may be a linear-movement device that is mounted insidehousing 20 and configured to selectively extend and retract to movecompactor 164 between its engaged position and the threading ordisengaged position. In the disclosed embodiment, actuator 166 is atwo-position pneumatic cylinder. It is contemplated, however, thatactuator 166 could alternatively be a solenoid plunger, an electricmotor/leadscrew mechanism, or another device having any number ofdifferent positions. Actuator 166 may include a cylinder, and a pistonhaving a rod extending therefrom. The rod of the piston may extend fromhousing 20 toward compactor 164, and pivotally connect to bracket 180(e.g., via pin 172). The rod of the piston may also be slidinglysupported by frame 162 via a slide cover 183 that is affixed (e.g., viathreaded fastening) to an outer end surface of frame 162. As pressurizedair (or another medium) is introduced into a first chamber of thecylinder, the piston may extend from the cylinder, causing the rod toslide away from the cylinder through cover 183 and push bracket 180 tothe engaged state. In contrast, as pressurized air is introduced into asecond chamber of the cylinder the piston may be retracted into thecylinder, causing the rod to slide back toward the cylinder and retractbracket 180 to the disengaged or threading position.

In one embodiment, a spring-biased lash adjuster 185 forms a link withinthe piston rod. This may allow the pivoting motion of bracket 180 and/orthe pressure exerted by compactor 164 on discharging material to beadjusted. It is contemplated that lash adjuster 185 may be a manualadjustment device or an automated adjustment device, as desired.

In one embodiment, a scraper 184 may be associated with compactor 164,and function to remove residual matrix (cured and/or uncured) from thesurface of roller 178. In the disclosed example of FIGS. 10-12, scraper184 is mounted to bracket 180 at a trailing side of roller 178 (e.g.,opposite the discharging reinforcements) and extends to or nearly to thesurface of roller 178. Scraper 184 may be removably connected to bracket180 (e.g., via one or more fasteners 186), such that scraper 184 mayeasily be adjusted, cleaned, repaired and/or replaced.

Also in some embodiments, a tag-end support or final guide 188 may beprovided adjacent roller 178 that is configured to support and guide thetag-end of a reinforcement after the reinforcement has been severed bycutting module 26. In particular, it may be possible under somecircumstances (e.g., when head 16 is tilted in a leading direction) forthe tag-end to flop down onto the print surface after being severed,before roller 178 has an opportunity to roll over and compress thematerial. In these circumstances, instead of the tag-end flopping ontothe print surface, the tag-end may flop into support 188 and/or be heldagainst (e.g., wrapped around) roller 178. This may allow the tag-end tosubsequently be pulled down and compressed onto the print surface,without discontinuity in print quality. In the disclosed embodiment,tag-end support 188 is a flat or curved plate mounted to frame 162(e.g., via a pin 189) that extends back toward roller 178. It iscontemplated, however, that tag-end support 188 could alternativelyembody a rod, a lever, or an arm and/or extend forward from roller 178or bracket 180. It is also contemplated that tag-end support 188 mayalso be movable between an extended position (shown in FIG. 12) and astowed position, as desired. For example, movement of compactor 164 tothe retracted or threading position may also function to move tag-endsupport 188 to the stowed position, thereby providing increasedclearance for threading purposes.

Curing module 30 may include any combination of components situated atany convenient location to cure the matrix coating the reinforcements,after compacting module 28 has compacted the discharging material. Inthe disclosed embodiment, curing module 30 includes a source 190 of cureenergy, and one or more transmission lines 192 extending from source 190to a point of exposure 194 adjacent roller 178. In the disclosedembodiment, the cure energy is UV light and/or laser energy. In oneexample, the energy is generated by one or more LEDs and/or lasersassociated with source 190, and transmission lines 192 are fiber opticsthat transmit the energy to the point of exposure 194. One or morebrackets 196 may be mounted at the point of exposure 194 (e.g.,connected to frame 162 and/or bracket 180), and used to secure and/oraim the distal ends of the fiber optics. It is contemplated thatdifferent or additional sources 190 may be utilized in place ofUV-generating LEDs or lasers, if desired. For examples, sources ofmicrowave energy, heat energy, vibrational energy, chemical energy, etc.could be used. It is also contemplated that transmission lines 192 maybe omitted in some embodiments.

INDUSTRIAL APPLICABILITY

The disclosed system and print head may be used to continuouslymanufacture composite structures having any desired cross-sectionalsize, shape, length, density, and/or strength. The composite structuresmay include any number of different reinforcements of the same ordifferent types, diameters, shapes, configurations, and consists, eachcoated with a common matrix. Operation of system 10 will now bedescribed in detail with reference to FIGS. 1-3.

At a start of a manufacturing event, information regarding a desiredstructure 12 may be loaded into system 10 (e.g., into controller 21 thatis responsible for regulating operations of support 14 and/or head 16).This information may include, among other things, a size (e.g.,diameter, wall thickness, length, etc.), a shape, a contour (e.g., atrajectory), surface features (e.g., ridge size, location, thickness,length; flange size, location, thickness, length; etc.) and finishes,connection geometry (e.g., locations and sizes of couplings, tees,splices, etc.), location-specific matrix stipulations, location-specificreinforcement stipulations, etc. It should be noted that thisinformation may alternatively or additionally be loaded into system 10at different times and/or continuously during the manufacturing event,if desired. Based on the component information, one or more differentreinforcements and/or matrixes may be selectively supplied to head 16(e.g., from an onboard source or from a remote or offboard source—notshown). The reinforcements may then be threaded through head 16 prior tostart of the manufacturing event.

Threading of head 16 may include passing (e.g., by way of open door 42)of the reinforcements from the top of the image shown in FIG. 3 andthrough guiding module 22 (e.g., between entrant rollers 52) downward.At this point in time, piloting subassembly 54 may also be open (e.g.,cover 74 and latching mechanism 76 may be removed), such that thereinforcements may be placed at desired locations relative to features82 (e.g., between particular dividers and/or within specificgrooves—referring to FIG. 5). Cover 74 and latching mechanism 76 maythereafter be re-secured in place over channeling base 72.

Additional lengths of reinforcements may then be pulled through guidingmodule 22 and led into feeding module 24. Specifically, thereinforcements may be pulled through the space between feed rollers 98,which may be in their disengaged orientations at this point in time. Thereinforcements may then be pulled further (e.g., from the tip of head16), until they reach compactor roller 178. Compactor roller 178 may bein its disengaged state at this time, such that greater clearance isprovided for threading. After threading is complete, compactor roller178 may be pushed forward to its engaged state, and head 16 may be readyto discharge matrix-coated reinforcements. Tag-end support 188 may holdthe free end of the reinforcements against roller 178 at this point intime.

Head 16 may then be moved by support 14 under the regulation ofcontroller 21 to cause matrix-wetted reinforcements to be placed againstor on a corresponding anchor point 18 (referring to FIG. 1). Curingmodule 30 may then be selectively activated to cause hardening of thematrix surrounding the reinforcements, thereby bonding thereinforcements to anchor point 18. Thereafter, head 16 may be moved inany trajectory to pull wetted-reinforcements from head 16 onto existingsurfaces and/or into free space to form structure 12.

The component information may be used to control operation of system 10.For example, the reinforcements may be discharged from head 16 (alongwith the matrix), while support 14 selectively moves head 16 in adesired manner during curing, such that an axis of the resultingstructure 12 follows a desired trajectory (e.g., a free-space,unsupported, 3-D trajectory). As the separate reinforcements are pulledthrough head 16, the reinforcements may pass under compactor 164 andthereafter be exposed to cure energy from curing module 30.

After a period of material discharging, it may be come necessary tosever the reinforcements (e.g., to complete the manufacturing eventand/or to move head 16 to another area of structure 12 for restart of anew track of discharging material). At this point in time, actuator 138may be selectively energized (e.g., by controller 21—referring toFIG. 1) to push anvil 136 downward (referring to the perspective ofFIGS. 8 and 9) past the serrated cutting edge 156 of blade 134, therebysevering the reinforcements. This may leave a tag-end of free materialwithin head 16 that is yet to be discharged and placed. The tag-end mayrest on and/or in support 188 (referring to FIG. 12), until additionalmovement of head 16 causes the material to be pulled out of head 16 andcompacted by compactor 164.

It has been found that, in some applications, clamping of thereinforcements prior to severing may be beneficial. For example,clamping may inhibit tension within the reinforcement from causingmovement after severing is complete. Accordingly, any type of clampingmechanism known in the art (not shown) could be located upstream and/ordownstream of blade 134 and anvil 136.

To thereafter restart discharging of a new track of material, support 14(under the regulation of controller 21) may move head 16 to thenew-start area. Compacting module 28 may be moved to its retractedstate, and feeding module 24 may selectively cause feed rollers 98 torotate to their engaged positions and push the new end of matrix-wettedreinforcements toward compactor 164. This may be considered part of astartup sequence that is implemented after every cut of thereinforcements and/or at the beginning of any print process. It shouldbe noted that head 16 may be maintained in a vertical orientation duringthe startup sequence, in some embodiments, such that the material beingpushed out by feed rollers 98 hangs in general alignment with the normaltravel path of wetted-reinforcements through head 16. This may help toavoid hang-ups inside of head 16. In general, feeding module 24 may beused primarily (e.g., only, in some embodiments) during the startupsequence. Other orientations of head 16 during the startup sequence mayalso be possible and beneficial.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed system andhead. Other embodiments will be apparent to those skilled in the artfrom consideration of the specification and practice of the disclosedsystem and head. It is intended that the specification and examples beconsidered as exemplary only, with a true scope being indicated by thefollowing claims and their equivalents.

What is claimed is:
 1. A print head for an additive manufacturingsystem, comprising: a receiving end configured to receive a matrix and acontinuous reinforcement; a discharging end configured to discharge thecontinuous reinforcement at least partially coated in the matrix; and afeeder located between the receiving end and the discharging end, thefeeder being configured to push the continuous reinforcement out of theprint head at only select times during discharge of the continuousreinforcement and the matrix.
 2. The print head of claim 1, wherein thefeeder is configured to push the continuous reinforcement and the matrixout of the print head only during a startup sequence.
 3. The print headof claim 1, wherein the feeder includes at least one eccentric camroller.
 4. The print head of claim 3, wherein the eccentric cam rollerincludes: a first portion having a first radius and being configured toengage the continuous reinforcement; and a second portion having asecond radius less than the first radius.
 5. The print head of claim 3,wherein an arc length of the first portion is equal to a length of thecontinuous reinforcement pushed out of the print head at the selecttimes.
 6. The print head of claim 5, further including: a compactingmodule located downstream of the eccentric cam roller; and a cuttingmodule located between the eccentric cam roller and the compactingmodule.
 7. The print head of claim 6, wherein the arc length is equal toa distance between the cutting module and the compacting module.
 8. Theprint head of claim 1, wherein: the eccentric cam roller is a firsteccentric cam roller; and the print head further includes a secondeccentric cam roller oriented in opposition to the first eccentric camroller.
 9. The print head of claim 8, further including an actuatorconfigured to drive rotation of at least the first eccentric cam roller.10. The print head of claim 9, further including a gear trainoperatively connecting the first eccentric cam roller to the secondeccentric cam roller.
 11. The print head of claim 8, wherein the firsteccentric cam roller is biased toward the second eccentric cam roller.12. A system for additively manufacturing a composite structure,comprising: at least one of a gantry and a robotic arm that moves in aplurality of directions during manufacturing of the composite structure;and a head coupled to the at least one of the gantry and the robotic armand including: a receiving end configured to receive a matrix and acontinuous reinforcement; a discharging end configured to discharge thecontinuous reinforcement at least partially coated in the matrix;eccentric cam rollers located between the receiving end and thedischarging end, the eccentric cam rollers being configured to push thecontinuous reinforcement out of the print head only during a startupsequence.
 13. The system of claim 13, wherein each of the eccentric camrollers includes: a first portion having a first radius and beingconfigured to engage the continuous reinforcement; and a second portionhaving a second radius less than the first radius, wherein an arc lengthof the first portion is equal to a length of the continuousreinforcement pushed out of the print head at the select times.
 14. Thesystem of claim 13, further including: a compacting module locateddownstream of the eccentric cam rollers; and a cutting module locatedbetween the eccentric cam rollers and the compacting module, wherein thearc length is equal to a distance between the cutting module and thecompacting module.
 15. A method of additively manufacturing a compositestructure, comprising: receiving a matrix and a continuous reinforcementat a first end of a print head; discharging the continuous reinforcementat least partially coated in the matrix from a second end of the printhead; and pushing the continuous reinforcement out of the print head atonly select times during discharge of the continuous reinforcement andthe matrix.
 16. The method of claim 15, wherein pushing the continuousreinforcement out of the print head at only select times includespushing the continuous reinforcement and the matrix out of the printhead only during a startup sequence.
 17. The method of claim 16, furtherincluding moving the print head to cause the continuous reinforcement tobe pulled out of the print head during discharging at times other thanduring the startup sequence.
 18. The method of claim 16, wherein pushingthe continuous reinforcement out of the print head includes pushing outa length of the continuous reinforcement that is equal to a distancebetween a cutting module and a compacting module of the print head. 19.The method of claim 18, further including exposing the matrix to a cureenergy at a location outside of the print head and downstream of thecompacting module.
 20. The method of claim 15, further including atleast partially coating the continuous reinforcement with the matrixinside of the print head.